1. Field of the Invention
The present invention relates to multi-color CMOS pixel sensors. More particularly, the present invention relates to multi-color CMOS pixel sensors with shared row wiring and dual output lines.
2. The Prior Art
Multi-color CMOS pixel sensors are known in the art. Such pixel sensors are often configured with more than one photodiode per color. This type of pixel sensor has a unique challenge that the pixel needs lots of wires compared to a conventional CMOS pixel sensor because photodiodes are stacked increasing the number of photodiodes per unit area. The number of wires are a problem because as the pixel sizes shrink there is less room for a large number of signal routing through the pixel array. There also is a trend to using fewer layers of metal as the pixels get smaller to improve the optical stack between the microlens to the photodiodes. This problem is further complicated by the fact that certain wires need to move through the array in different directions and each metal layer is only useful for moving in one direction through the array unless the layer the wire is running on changes to other layers to avoid congestion. The output wires are usually considered column wires in the art and run in one direction through the array. The row enable and color enable lines have to run through the array perpendicular to the output lines and this is considered the row direction through the array. The row and color enable signals are usually different for each row of the sensor to enable proper sharing of the column output signal and the photocharge collection node. The reset signal also has to run in the row direction through the array to enable rolling shutter readout and reset and is also unique for each row of the sensor.
The power signals Vpix and SFD can usually run in either direction through the array since they global signals and the same for the complete array. These power signals are usually run in the column direction since only the column output signal runs in that direction. For pixel architectures that have multiple photodiodes sharing a common photocharge collection node, amplifier and row enable transistor, like those described here, there can be a lot more signals that need to be routed through the array in the row direction than in the column direction.